Microwave transmission line



May 6, 1958 M. ARDlTl ETAL MICROWAVE TRANSMISSION LINE 2 sheets -sheet 1Filed May 8, 1952 sn RIN Y 0 w M N M R 5 0 Vm n NRK I M A A Y y 6, 1958M. ARDlTl ET AL 2,833,995

MICROWAVE TRANSMISSION LINE Filed May 8. 1952 2 Sheets-Sheet 2 INVENTORSMAURICE ARDITI JACK ELEFANT United States PatentO MICROWAVE TRANSMISSIONLINE Maurice Arditi, Clifton, N. J., and Jack Elefant, Brooklyn, N. Y.,assignors to International Telephone and Telegraph Corporation, acorporation of Maryland Application May 8, 1952, Serial No. 286,765

'9 Claims. (Cl. 333-97) This invention relates to microwave'transmissionlines and more particularly to a means for adjusting the wavelengthcharacteristic of a section of such line.

In the copending applications of D. D. Grieg and H. F. Engelmann, SerialNos. 227,896 .now abandoned, and 234,503 now Patent No. 2,721,312, filedMay 23, 1951, and June 30, 1951, respectively, and M. Arditi and P.Parzen, Serial No. 276,764, filed May 8, 1952, now Patent No. 2,774,046,a type of microwave transmission line is disclosed comprising, in one ofits simplest forms, two conductors printed or otherwise disposed insubstantially parallel relation on opposite sides of a strip or layer ofdielectric material a small fraction of a quarter wavelength thick. Thetwo conductors may be of the same width or one may be made wider thanthe other. The dielectric between the two conductors may be ofsubstantially the same width as the narrowest of the two conductors orwider according to the relationships desired.

An object of this invention is to provide a section of transmission lineof the parallel conductor type which is capable of adjustment in widthwhereby changes in line wavelength may be made.

Another object of this invention is to make a device for use intransmission lines which is capable of line wavelength adjustment.

One of the features of this invention is the provision of a section of aparallel conductor line with pieces of conductors overlying in parallelrelation one of the line conductors together with means for adjustingthe position of such pieces laterally with respect to the lineconductor. By this arrangement the eifective width of the line conductorcan be adjusted at will. By making the line conductor smaller where theoverlapping pieces are located, the line conductor can actually be madenarrower by adjusting the conductor pieces within the outline of theline conductor.

Another feature of the invention includes changing the effective widthof the dielectric strip and in some instances the widths of both thedielectric and conducors whereby changes in line wavelengh are obtained.Still other features include selective substitution of the linedielectric, and the use of a conductive screw either by itself or inconjunction with line width adjustable conducting pieces for producingchange in line wavelength.

The above-mentioned and other objects and features of this inventionwill become more apparent by reference to the following descriptiontaken in conjunction with the accompanying drawings, in which:

Fig. 1 is a plan view of a section of microwave transmission line withmeans for adjusting the effective width thereof in accordance with theprinciples of this invention, the section of line being shown in itsnarrowest adjusted width;

Fig. 2 is a plan view of the left-hand side of the line shown in Fig. 1with the effective line width adjusted to its maximum value;

Fig. 3 is a cross-sectional view taken substantially along line 33 ofFig. 2;

2,333,995 Patented May 6, 19 58 Fig. 4 is a graph showing changes inline wavelength in accordance with the different widths of the lineconductor;

Fig. 5 is a plan view of a modified form of transmission lineincorporating the principles of this invention;

Fig: 6 is a cross-sectional view taken along line =66 of Fig. 5

Fig. 7 is a plan view of a modified .form of the invention;

Fig. 8 is a longitudinal cross-section along line 8-8 of Fig. 7;

Fig. 9 is a plan view of still another embodiment; and Fig. 10 .isa'plan view of a dielectric'card usable in th form of Fig. 9.

Referring to Figs. 1, 2, and -3 of the drawing, the 'microfaces of thedielectric, .or by any other of the known printed circuit techniques.The spacing of the" two'conductors is preferably selected a smallfraction in the order of about -to about /5 of a quarter wavelength ofthe microwave propagated --therealong.

The conductor 1 is preferably narrowed gradually as indicated at 4 for adesired lengtheither l or 2 line wavelengths long. A pair of conductivestrips 5 and6 are disposed in overlapping relationship with respect tothe conductor '1. The combined widths of the two strips 5 and 6 arepreferably equal to the narrowest width-of the line conductor 1 althoughnot necessarily so. Centrally disposed at spaced points with respect tothe line conductor 1 are two posts 7 and 8 preferably of dielectricmaterial which may be the same as the dielectric The posts 7 and 8,however, may be of conductive material secured to the conductor ,2 atone end providing the posts are free of contact with the conductor 1 andthe conductor pieces 5 and 6. This maybe accomplished by providingenlarged openings 9 in the conductor 1 through which the posts extend.Likewise, the pieces 5 and 6 may be provided with cut-outs as indicatedat 10 and 11 to avoid contact with the post should the latter be ofconductive material. The position of such a post in the line is found tohave small eifect upon the line compared with the change in conductorwidth provided by adjustment of conductor pieces '5 and 6.

Pivotly mounted on these posts 7 'and'8 .are cams 12 and 12a, whichcontain a pair of cam slots '01 surfaces 13 and 14. The slots 13 and 14receive pins 15vand 16 carried by conductor pieces -5 and 6,respectively. Encircling the cams 12 and 12a is an endless cord '17.When either cam is manipulated 'by manually turning knob 18, both camsare rotated through means of the endless cord 17. This rotation of theearns 12 :and 12a causes movement of the conductor pieces 5 andfloutwardly or inwardly laterally of the conductor 1 depending upon thedirection of rotation of the cams. In the position shown in Fig. 1, thecams are shown at one extremity of their move in a direction such as todraw the conductor pieces -5 and 6 inwardly with respect to the outlineof the line conductor 1. In Fig. 2 the conductor pieces 5 and 6 areshown in their outward position'rwhen the cams are moved to the opposite:end of their movement. It will be observed that the pins 15 .and 16 areat one end of the cam slots 13 and 14 in Fig. land the opposite ends ofthe same slot in Fig. 2.

In order to maintain the conductor pieces 5 and 6 in good conductivecontact with the line conductor 1, the ends 19 and 20 are receivedbeneath a strap 21, 22. This strap may be formed of lateral extensionsof the conductor 1 bent back across the ends of the conductor pieces 5and 6 and soldered together as indicated at 23. The strap 21, 22 may beotherwise formed and in fact may constitute a plate of suitablematerial, either conductive or dielectric, as may be desired, carried byeither the conductor 1 or the dielectric 3. Regardless of, the structural arrangement of the strap 21, 22, the purpose thereof is to holdthe ends 19 and 20 flat against the conductor 1 so as to insureconductive contact, and yet to provide sufiicient resilience to allowlateral movement of the pieces 5 and 6.

As hereinbefore described, the edges of the conductor 1 are graduallytapered inwardly to the narrowest cross section desired for theconductor 1. The end portions of the conductor pieces 5 and 6 arelikewise curved gradually as indicated at 24 and 25 so as to avoid anyabrupt discontinuity between the edge of the conductor 1 and the edgesof the two pieces 5 and 6. This gradual transition holds substantiallythroughout the extent of adjustment.

In Fig. 4 a graph of the line wavelength for different line widths isshown for two different materials. The curve 26 was determined by meansof a printed microwave transmission line using polystyrene as thedielectric 3. Curve 27 was determined from a transmission line sectionusing fiberglass as the dielectric 3. The frequency employed for thesetests was 4700 mc./s. A change in width of the line conductor 1 from 6mm. to 3 mm. in the case of the fiberglass specimen increased the linewavelength from 36.3 mm. to 38.3 mm. The same change in conductor widthfor the specimen utilizing polystyrene dielectric was from 45 mm. to 48mm.

The changing of the width of the dielectric material while leaving theconductors the same width also produces a change in the line wavelength.By extending the width of the dielectric strip from a width equal to thewidth of two conductors of the same width by 27 mm. in oppositedirections, a line wavelength was varied from 35.2 mm. to 36.8 mm. InFig. 5 a transmission line is shown wherein the conductors 28 and 29 areof substantially the same width separated by a similar width ofdielectric material 30. The side edges of the dielectric strip 30 mayhave small recesses 31 and 32 whereby additional strips of dielectricmaterial 33 and 34 may be applied by means of dielectric pins receivablein the recesses 31 and 32. However, any suitable means may be providedto secure these additional strips, one simple method being to use abonding lacquer. Two or more of such additional dielectric strips may beadded as indicated by the additional strips 35 and 36. In this way theline wavelength may be increased as desired. The additional strips 3336would of course be provided with tapered end portions so as to present agradual transition from the width of the strip 30 to the combined widththerewith of the additional strips of dielectric. If desired theseadditional strips of dielectric may also carry strips of conductors asindicated at 33a, 33b and 34a, 34b. These additional conductor stripsmay be on one side only of the additional dielectric strips or on bothsides as may be desired.

Figs. 7 and 8 show a further embodiment of the invention wherein adouble line wavelength efiect is obtained simultaneously. One effect isobtained by a conductive screw 37 and the other is obtained by a pair ofconductive pieces 38 and 39 similar to those shown in Figs. 1 to 3. Thescrew 37 is provided with gear teeth 40 which mesh with racks 41 and 42carried by the pieces 38 and 39, respectively. The screw 37 isthreadably received in a hole 43 and when turned therein it activatesracks 41 and 42 to move the pieces 38 and 39 laterally to effect achange in the eifective width of the line conductor 1a. The introductionof screw 37 into the space between conductors 1a and 2a also effects asmall change in the width characteristic of the line conductor. Forexample, a conductive screw of 0.05 in diameter inserted substantiallyentirely across the space between conductors corresponds to an increaseof approximately 0.008 in the line wavelengths.

The threads of the screw 37 may be such as to cause screw movement intothe line when pieces 38 and 39 are moved apart, or vice versa, the screwmay move out of the line when pieces 38 and 39 are moved apart. In thefirst instance the two effects are additive and in the second instancethe effect of the screw would be subtractive with respect to the etfectof pieces 38 and 39. Ribs 44 and 45 are provided on conductor in toguide the pieces 38 and 39.

In Fig. 9 we show still another embodiment wherein the widening effector line wavelength is varied by selectively changing the dielectric inthe line. A section of the dielectric 3b is replaced by a card 46 madeup of a plurality of strips 47, 48 and 49 of materials having differentdielectric constants. By selectively placing the card between conductors1b and 2b a variation in line wavelength may be obtained in accordancewith the particular dielectric constant of the strip introduced inalignment with the dielectric 30. Air dielectric may be had by removingthe card but then the abrupt change between dielectric 3b and airproduces an impedance mismatch unless the spacing between conductors isreduced. Where a card section is of foam dielectric having adistribution of air spaces therethrough, as indicated by section 49, thesame impedance matching problem is present. We overcome this, however,by making that section of the card denser at the ends of the stripthereby presenting a gradual transition between dielectric 3a and theless dense foam in the center portion of the section 49. As a furthervariation the card 45 may be replaced by a card of a particulardielectric and if desired the card may be specially shaped to produce agradual transition as indicated by the card 50 of Fig. 10. The change indielectric width to a dimension less than the width of the lineconductor 1b introduces air as part of the effective dielectric.

While we have described above the principles of our invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made by way of example only and not as a limitationto the scope of our invention as set forth in the objects thereof and inthe accompanying claims.

- We claim:

1. A transmission line comprising first and second ribbon-likeconductors, means disposing said conductors in spaced substantiallyparallel relation, and means for adjusting the line wavelength of asection of said line including a piece of conductor having an elongatedflat surface disposed in longitudinal overlying parallel contactrelation to said first conductor and means for adjusting the position ofsaid piece of conductor laterally to extend beyond said first conductorand confront said second conductor to thereby widen the conductorcharacteristics of said first conductor relative to said secondconductor.

2. A transmission line according to claim 1, wherein said piece ofconductor has tapered end portions to insure a gradual transition withrespect to said first conductor when said piece of conductor extendsbeyond the edge of said first conductor.

3. A transmission line comprising first and second ribbon-likeconductors, means disposing said conductors in spaced substantiallyparallel relation, and means for adjusting the line wavelength of asection of said line including a pair of conductor pieces each having anelongated flat surface disposed in longitudinal overlying paralleljuxtaposed relation to said first conductor and means for adjusting thepositions of said pieces laterally to extend beyond said first conductorand confront said second conductor to thereby 'widen the conductorcharacteristics of said first conductor relative to said secondconductor. I

4. A transmission line according to claim 3, wherein the means foradjusting the position of said pieces of conductor comprises a camcarried by the transmission line, means carried by each of saidconductor pieces for engagement with said cam and means for turning thecam to efiect movement of said conductor pieces.

5. A transmission line according to claim 4, further including means formaintaining said conductor pieces in conductive contact with said firstconductor.

6. A transmission line comprising first and second ribbon-likeconductors, said second conductor being Wider than said first conductor,a strip of dielectric material separating said conductors in spacedsubstantially parallel relation a small fraction of a wavelength apart,and means for adjusting the width of said first conductor including apair of conductor strips disposed in overlying contact relationship withrespect to said first conductor and means for adjusting the positions ofsaid pieces laterally to vary the overall width of said first conductor.

7. A transmission line comprising first and second ribbon-likeconductors, said second conductor being wider than said first conductor,a strip of dielectric material separating said conductors in spacedsubstantially parallel relation a small fraction of a wavelength apart,and means for adjusting the width of said first conductor, said firstconductor comprising a section tapered from its normal width to a givennarrow width and the means for adjusting the width of said firstconductor includes a strip of conductor overlying said first conductorand means to adjust the position of said conductor strip laterally ofsaid first conductor to project outwardly beyond the edge of said firstconductor, the end portions of said conductor strip being tapered toprovide a gradual transition with the edge of said first conductor.

8. A transmission line comprising first and second ribbon-likeconductors, means disposing said conductors in spaced substantiallyparallel relation, means for adjusting the line wavelength of a sectionof said line including a piece of conductor having an elongated flatsurface disposed in longitudinal overlying parallel contact relation tosaid first conductor, means for adjusting the position of said piece ofconductor laterally to extend beyond said first conductor and confrontsaid second conductor to thereby Widen the conductor characteristics ofsaid first conductor relative to said second conductor,

said adjusting means including a conductive screw threadably adjustablethrough one of said conductors relative to the other.

9. A transmission line comprising first and second ribbon-likeconductors, means disposing said conductors in spaced substantiallyparallel relation a small fraction of a quarter wavelength apart, meansfor adjusting the line wavelength of a section of said line including apair of conductor pieces having elongated flat surfaces in longitudinaloverlapping contact relation to said first conductor, means foradjusting the position of said conductor pieces laterally to extendbeyond said first conductor and confront said second conductor tothereby widen the conductor characteristics of said first conductor,said adjusting means including means guiding said conductor pieces forsaid lateral movement, a rack carried by each said piece and aconductive screw threadably received through said first conductor foradjustment relative said second conductor and gear teeth carried by saidscrew to activate said racks.

References Cited ,in the file of this patent UNITED STATES PATENTS2,297,266 Viewager Sept. 29, 1942 2,402,624 Himmel June 25, 19462,405,174 Alford Aug. 6, 1946 2,411,534 Fox Nov. 26, 1946 2,424,982Higgins Aug. 5, 1947 2,433,368 Johnson Dec. 30, 1947 2,521,873 RobertsonSept. 12, 1950 2,540,488 Mumford Feb. 6, 1951 2,611,822 Bliss Sept. 23,1952 FOREIGN PATENTS 665,803 Great Britain Aug. 1, 1951

